This invention relates to normally tacky and pressure-sensitive adhesive tape, especially tape having utility as a closure for disposable diapers.
While disposable diapers have been commercially available for at least the past 30 or 40 years, their use has increased dramatically in the last decade. Much of the present commercial success of disposable diapers can be attributed to the development of pressure-sensitive adhesive tape closure systems which replace the safety pins that had been employed for more than a century.
Disposable diapers typically comprise an absorbent filler material and an outer moisture-impervious polyethylene film. The diapers are generally so configured that when they are placed on an infant, they are folded so that two adjacent edges are either juxtaposed or overlapped, with a strip of normally tacky and pressure-sensitive adhesive tape being used to hold the edges together.
In applying a disposable diaper to a baby, a parent typically shakes talcum powder on one hand, rubs his hands together, and then transfers the powder from his hands to the baby. In the process, the polyethylene film is often sprinkled with powder. The diaper is then folded into position, at which time the strip of pressure-sensitive adhesive tape, normally attached to and folded around one edge of the diaper, is unfolded and applied to the opposite edge. Talcum powder (talc), however, contaminates the surface of conventional pressure-sensitive adhesives so that their ability to adhere is greatly reduced. This loss of adhesive properties is especially pronounced in the case of those adhesives which are most commonly employed in the manufacture of tape products; indeed, talc is often used to reduce tackiness, e.g., by applying it to the sticky edges of rolls of tape.